As demand for ever-shrinking semiconductor devices continues to increase, so too will the demand for improved semiconductor wafer inspection systems. The fabrication of semiconductor devices, such as logic and memory devices, typically includes processing a semiconductor wafer using a large number of semiconductor fabrication processes to form various features and multiple levels of the semiconductor devices. Multiple semiconductor devices may be fabricated in an arrangement on a single semiconductor wafer and then separated into individual semiconductor devices.
Various inspection system features and techniques have been employed to improve defect detection sensitivity for both reticles and wafers. One example is to decrease the wavelength of the illumination light that is being used to detect defects. As the wavelength decreases, smaller defects can generally be detected. However, there are limits to how short a wavelength can be used without the system configuration becoming too impractical, complex, or expensive. Another parameter of the inspection tool that affects defect detection sensitivity is the system's numerical aperture (NA). Unfortunately, the NA is often limited to a theoretical maximum of 1.0 for imaging in air or the system becomes too impractical to build and maintain.
There continues to be a need for improved systems and techniques for increasing sensitivity for defect detection.